1. Field of the Invention
The present invention relates to an integrated circuit, a fabricating method of the integrated circuit and an evaluating method of the integrate circuit, more particularly, to an integrated circuit including an IC (integrated circuit) chip using a semi-insulating substrate and a ceramic substrate on which the IC chip is put and the integrated circuit which can be evaluated as to a bonding condition between the IC chip and the substrate, and to a fabricating method and an evaluating method thereof.
2. Description of the Related Art
As known, when an integrated circuit is fabricated, a processing step called a die bonding is performed. The die bonding is a step that a chip (also called a die) divided in a dicing step is fixed to a substrate. It is known that there are three bonding methods such as a paste bonding, a solder bonding and an eutectic bonding.
In an integrated circuit fabricated by mounting an IC chip using semi-insulator such as GaAs or InP on a ceramic substrate, there are many cases that the solder bonding and the eutectic bonding are used for bonding the IC chip and the ceramic substrate. In the solder bonding, a foil of low melting point alloy (namely, solder) is put between the chip and the substrate. Then, the foil is reflowed by heating, whereby the chip and the ceramic substrate are bonded. Additionally, in the solder bonding, for example, when the wettability of the solder is not good for chip materials or a ceramic substrate, films including materials of which the wettabilities are good are previously formed on one or both of bonding surfaces of the chip and the ceramic substrate by a vacuum evaporation method or the like.
In the eutectic bonding, the chip and the ceramic substrate are bonded by using a diffuse reaction between two elements which form an eutectic alloy. That is, in the eutectic bonding, as shown in FIGS. 9(A) and 9(B), a chip 31 of which a bonding surface is provided with a film 32 including one of the two elements to be an eutectic alloy and a ceramic substrate 34 of which a bonding surface is provided with a film 33 including another element are made contact (see FIG. 9(A)) and heated temporarily, so that the chip 31 and the ceramic substrate 34 are bonded by an eutectic alloy 35 (and the film 33) (see FIG. 9(B)). In FIGS. 9(A) and 9(B), all the film 32 is changed into an eutectic alloy, however, there is a case that the film 32 remains.
In the solder bonding or the eutectic bonding, a bonding portion with very small thermal resistance can be formed. In the eutectic bonding, however, as shown in FIG. 10, there is a case in that the eutectic alloy layer 35 is not evenly formed, so that a defect such as a cavity 50 is formed between the chip 31 and the ceramic substrate 34. In the solder bonding, there is also a case in that a cavity 50 is formed in a bonding portion.
In an integrated circuit like shown in FIG. 10, a thermal resistance between the chip 31 and the ceramic substrate 34 (particularly, around the cavity 50) is high therefore, when this integrated circuit operates, the temperature of the chip 31 raises compared with an integrated circuit of which a bonding portion in normally formed, shown in FIG. 9(B).
Particularly, in an IC chip using a semi-insulating or insulating substrate such as GaAs (gallium arsenide), InP (indium phosphorus) and sapphire, the thermal conductivity of the substrate is low, therefore, when the chip is not normally bonded to the ceramic substrate, the circuit fabricated on the chip becomes not to operate normally because of the increased temperature.
Thus, it is desirable to select integrated circuits which are not normally bonded. In conventional integrated circuits, a bonding condition is evaluated only by measuring the force required to peel the chip from the ceramic substrate or measuring the thermal resistance actually. The former is a destructive inspection, therefore, bonding conditions of the integrated circuits can not be evaluated individually by the former method. The latter is a non-destructive inspection, and can be used for integrated circuits individually, however, it takes a long time to measure the thermal resistance. Thus, in the latter method, there is no choice except for that some of plural integrated circuits are evaluated as samples.
Accordingly, it is an object of the present invention to provide an integrated circuit of which a boding state can be simply evaluated. It is another object of the present invention to provide a fabricating method of an integrated circuit of which a boding state can be simply evaluated.
To solve the above described problems, in the present invention, an integrated circuit, which comprises a semiconductor chip having active elements on a main face and a substrate having an electrode on a main face and a bonding layer formed by alloying the electrode and a conductive member lied between a rear face opposite to the main face of the semiconductor chip and the main face of the substrate, is fabricated with employing the semiconductor chip including at least two surface electrodes formed on the main face, and connection wiring portions provided by filling at least two holes respectively formed below the surface electrodes so as to penetrate the semiconductor chip from the main surface to the rear face with conductive materials.
According to the integrated circuit fabricated like this, a resistance between the surface electrodes provided on the semiconductor chip is measured, whereby the bonding condition between the semiconductor chip and the substrate can be evaluated, therefore, when all integrated circuits are fabricated to be this structure, it can be determined simply whether inferior or not.
Moreover, when the integrated circuit of the present invention is fabricated, the semiconductor chip which has a slit dividing a surface of the rear face into two may be used, and surface electrodes provided with an area capable of being touched with at least two external terminals may be used.
A first fabricating method of an integrated circuit is that of an integrated circuit including a semiconductor chip having active elements on a main face and a substrate having an electrode on a main face. The method comprises (a) forming at least two surface electrodes on the main face of the semiconductor chip, (b) forming connection wiring portions by making holes penetrating the semiconductor chip from a rear face opposite to the main face to the surface electrodes on the main surface and filling the holes with conductive materials, (c) forming two alienated conductive members on the rear face of the semiconductor chip, and (d) bonding the semiconductor chip with the substrate by putting the semiconductor chip on the substrate in a manner that the rear face of the semiconductor chip is opposite to the main face of the substrate and heating them.
According to this fabricating method, a resistance between the surface electrodes provided on the semiconductor chip is measured, whereby an integrated circuit which the bonding condition between the semiconductor chip and the substrate can be evaluated can be fabricated, therefore, when all integrated circuits are fabricated by this method, it can be determined whether a fabricated integrated circuit is inferior or not. Further, the two alienated conductive members are formed, therefore, when the bonding is not performed normally by any cause, a resistance between the surface electrodes becomes larger than a case in that an even conductive member is provided on the rear face of the semiconductor chip. Thus, it becomes easier to determine whether inferior or not. Additionally, when this fabricating method is used, it is desirable that two materials (elements) to be eutectic are used as the electrodes and the conductive members, however, it is also possible to use the same material (low melting point metal or alloy). Further, each of the surface electrodes is formed so as to be provided with an area capable of being contact with at least two external terminals, whereby it becomes possible to measure a resistance by the so-called four terminal method. Thus, it becomes possible to evaluate the bonding condition under no influence of the contact resistance. That is, though a difference of conditions in bonding portions is slight, an integrated circuit which the difference can be determined can be fabricated.
A second fabricating method of an integrated circuit is that of the integrated circuit including a semiconductor chip having active elements on a main face and a substrate having electrodes on a main face. The method comprises (a) forming four surface electrodes on the main face of the semiconductor chip, (b) forming connection wiring portions by making holes penetrating the semiconductor chip from a rear face opposite to the main face to the surface electrodes and filling the holes with conductive materials, (c) forming a groove portion dividing the surface of the rear face of the semiconductor into two, (d) providing conductive members on the rear face of the semiconductor chip expect for the groove portion, (e) forming the electrodes on the main face of the substrate in a manner that surface of the main face of the substrate is separated into two parts extending in a direction perpendicular to the groove portion, and (f) bonding the semiconductor chip and the substrate by putting the semiconductor chip on the substrate in a manner that the rear face of the semiconductor chip is opposite to the main face of the substrate and heating them.
According to this fabricating method, it becomes possible to obtain an integrated circuit in which conditions at various ranges in the bonding portion of the chip and the ceramic substrate can be evaluated with the combination of the four surface electrodes provided on the semiconductor chip. It also becomes possible to measure the resistance of the integrated circuit by the four terminal method or a bridge circuit, therefore, the bonding condition (resistance) can be detected under no influence of the contact resistance.
A first evaluating method of an integrated circuit intends to use for the integrated circuit including a semiconductor chip which has active elements on a main face and a substrate which has electrodes on a main face. The integrated circuit is fabricated by (a) a step of forming at least two surface electrodes on the main face of the semiconductor chip, (b) a step of forming connection wiring portions by making holes penetrating the semiconductor chip from a rear face opposite to the main face to the surface electrodes and filling the holes with conductive material, (c) a step of forming two alienated conductive members on the rear face of the semiconductor chip, and (d) a step of bonding the semiconductor chip and the substrate by putting the semiconductor chip on the substrate in a manner that the rear face of the semiconductor chip is opposite to the main face of the substrate and forming a bonding layer with alloying the conductive materials and the electrodes. Evaluation of a connecting condition between the semiconductor chip and the substrate is carried out by measuring resistance values between the surface electrodes or between one of the surface electrodes and the bonding layer.
A resistance value or the like between the surface electrodes or between one of the surface electrodes and the alloy layer is measured, whereby a condition of an alloy layer generated by alloying, namely, a connecting condition between the semiconductor chip and the substrate is evaluated.
Additionally, when this evaluating method is performed, it is desirable that each surface electrode is formed to be provided with an area capable of being contact with at least two external terminals, and the connecting condition between the semiconductor chip and the substrate is evaluated by applying a predetermined voltage between the surface electrodes with a pair of the external terminals and by measuring a voltage drop between the surface electrodes or between one of the surface electrodes and the bonding layer with another pair of the external terminals.
A second evaluating method of an integrated circuit intends to use for the integrated circuit including a semiconductor chip which has active elements on a main face and a substrate which has electrodes on a main face. The integrated circuit is fabricated by (a) a step of forming four surface electrodes on the main face of the semiconductor chip, (b) a step of forming connection wiring portions by making holes penetrating the semiconductor chip from a rear face opposite to the main face to the surface electrodes and filling the holes with conductive materials, (c) a step of forming a groove portion dividing the surface of the rear face of the semiconductor into two, (d) providing conductive members on the rear face of the semiconductor chip expect for the groove portion, (e) forming the electrodes on the main face of the substrate in a manner that surface of the main face of the substrate is separated into two parts extending in a direction perpendicular to the groove portion, and (f) bonding the semiconductor chip and the substrate by putting the semiconductor chip on the substrate in a manner that the rear face of the semiconductor chip is opposite to the main face of the substrate and forming a bonding layer with alloying the conductive materials and the electrodes. Evaluation of a connecting condition between the semiconductor chip and the substrate is carried out by measuring resistance values between the surface electrodes with contacting external terminals to the four surface electrodes in a manner that a bridge circuit is constructed.